The variability in the summer Arctic cloud-capped boundary layer

Michael Tjernstrom

CIRES Visiting Fellow

Abstract

Of all climate regimes, that in the central Arctic is
probably the least understood, primarily because of a
lack of all sorts of observations. This poses a problem
when developing parameterizations for, for example,
global climate models. Parameterizations build on the
ensemble of observations available on a particular sub-
grid scale process. If processes in a region of the Earth,
like the Arctic, are different than in other regions
and there is a lack of appropriate data to build
parameterizations, then it is no great surprise
if global models have problems in that reagion.

In this seminar aspects of boundary-layer variability
that are on the sub-grid scale in most models
will be discussed using data from a field experiment in
the Arctic on the Swedish icebreaker Oden. The talk will
focus on two aspects: the dirunal variation and mesoscale
variations. In both cases there appears to be links to
drizzle formation in the shallow but persistent Arctic
summer stratocumulus, which then links the observed
variability to peculiarities in the cloud microphysics
and aerosol formation. I will argue that if the climate
of the Arctic changes, so that its aerosol environment
becomes more similar to that at lower latitudes, clouds
may perhaps generate a negative feedback to climate
warming; probably the only (or maybe one of a few) in
the Arctic.